Implement my experimental arcfour modes. The 256-bit version is disabled

[u/mdw/putty] / ssharcf.c

diff --git a/ssharcf.c b/ssharcf.c
new file mode 100644 (file)
index 0000000..5946488
--- /dev/null
+++ b/ssharcf.c
@@ -0,0 +1,127 @@
+/*
+ * Arcfour (RC4) implementation for PuTTY.
+ *
+ * Coded from Schneier.
+ */
+
+#include <assert.h>
+#include "ssh.h"
+
+typedef struct {
+    unsigned char i, j, s[256];
+} ArcfourContext;
+
+static void arcfour_block(void *handle, unsigned char *blk, int len)
+{
+    ArcfourContext *ctx = (ArcfourContext *)handle;
+    unsigned k;
+    unsigned char tmp, i, j, *s;
+
+    s = ctx->s;
+    i = ctx->i; j = ctx->j;
+    for (k = 0; k < len; k++) {
+       i  = (i + 1) & 0xff;
+       j  = (j + s[i]) & 0xff;
+       tmp = s[i]; s[i] = s[j]; s[j] = tmp;
+       blk[k] ^= s[(s[i]+s[j]) & 0xff];
+    }
+    ctx->i = i; ctx->j = j;
+}
+
+static void arcfour_setkey(ArcfourContext *ctx, unsigned char const *key,
+                          unsigned keybytes)
+{
+    unsigned char tmp, k[256], *s;
+    unsigned i, j;
+
+    s = ctx->s;
+    assert(keybytes <= 256);
+    ctx->i = ctx->j = 0;
+    for (i = 0; i < 256; i++) {
+       s[i] = i;
+       k[i] = key[i % keybytes];
+    }
+    j = 0;
+    for (i = 0; i < 256; i++) {
+       j = (j + s[i] + k[i]) & 0xff;
+       tmp = s[i]; s[i] = s[j]; s[j] = tmp;
+    }
+}
+
+/* -- Interface with PuTTY -- */
+
+/*
+ * We don't implement Arcfour in SSH-1 because it's utterly insecure in
+ * several ways.  See CERT Vulnerability Notes VU#25309, VU#665372,
+ * and VU#565052.
+ * 
+ * We don't implement the "arcfour" algorithm in SSH-2 because it doesn't
+ * stir the cipher state before emitting keystream, and hence is likely
+ * to leak data about the key.
+ */
+
+static void *arcfour_make_context(void)
+{
+    return snew(ArcfourContext);
+}
+
+static void arcfour_free_context(void *handle)
+{
+    sfree(handle);
+}
+
+static void arcfour_stir(ArcfourContext *ctx)
+{
+    unsigned char *junk = snewn(1536, unsigned char);
+    memset(junk, 0, 1536);
+    arcfour_block(ctx, junk, 1536);
+    memset(junk, 0, 1536);
+    sfree(junk);
+}
+
+static void arcfour128_key(void *handle, unsigned char *key)
+{
+    ArcfourContext *ctx = (ArcfourContext *)handle;
+    arcfour_setkey(ctx, key, 16);
+    arcfour_stir(ctx);
+}
+
+static void arcfour256_key(void *handle, unsigned char *key)
+{
+    ArcfourContext *ctx = (ArcfourContext *)handle;
+    arcfour_setkey(ctx, key, 32);
+    arcfour_stir(ctx);
+}
+
+static void arcfour_iv(void *handle, unsigned char *key)
+{
+
+}
+
+const struct ssh2_cipher ssh_arcfour128_ssh2 = {
+    arcfour_make_context, arcfour_free_context, arcfour_iv, arcfour128_key,
+    arcfour_block, arcfour_block,
+    "arcfour128-draft-00@putty.projects.tartarus.org",
+    1, 128, "Arcfour-128"
+};
+
+const struct ssh2_cipher ssh_arcfour256_ssh2 = {
+    arcfour_make_context, arcfour_free_context, arcfour_iv, arcfour256_key,
+    arcfour_block, arcfour_block,
+    "arcfour256-draft-00@putty.projects.tartarus.org",
+    1, 256, "Arcfour-256"
+};
+
+/*
+ * arcfour256-draft-00@putty.projects.tartarus.org is as-yet untested
+ * against any other implementation, and hence is commented out.
+ */
+static const struct ssh2_cipher *const arcfour_list[] = {
+/*  &ssh_arcfour256_ssh2, */
+    &ssh_arcfour128_ssh2,
+};
+
+const struct ssh2_ciphers ssh2_arcfour = {
+    sizeof(arcfour_list) / sizeof(*arcfour_list),
+    arcfour_list
+};